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April l0, 1928. 1,666,059

E.GR1SS1NGER SOUND PROJECTOR Filed Dec. l2. 1923 2 Sheets-Sheet lHIM...A /l

g (By M60,

MATYORNEY Aprill, 1928.

E. GRISSINGER- SOUND 'PROJECTOR Filed Dec. l2, 1923 2 Sheets-Sheet n INV ENTOR M ATTORNEY CJi Patented Apr. 10, 1928.

Unirse srarss attese Ferca.

PATENT,

EIJWOOD GRISSINGER, OF BUFFALO, NEW YORK;

SOUND PROJECTOR.

Application led December 12. 1923. 'Serial'No G8,9v1.

sound projector peculiarly adapted to serve the purpose of an amplierfor phonographs but certainV features of tlieprojector will be founduseful in connection with radio and other telephonel receivers andother,vibratory sound producers and also in connection lwith other sources ofsound, :particularly Where, as in the case of human speech and music,the'soundseomprise a wide range of frequencies, and particularlyvwherefil i is desired to faithfully reproduce a multiplicity of sets ofwaves or complex. waves-of many frequencies` sin'iultaneously.l i

4A specificv object of my invention is to proivideiun air columnassociated atoneend with the'diaphragm of therphonograph re producer undat the other end communicating \v.i lli,the open air, vin Which Athe air`e'oluii1n .will he a suitablev medium for dcvelo'pinent, expansion ofwavefront, and

'i .projectingrv into the open air,sound waves having a wide range ofphysical lengthsy,ziri cluding sound waves of which the quarter nave.length 4is long, and requires great vlength of air column, and alsoshort-,Waves of y the higher frequencies, the, quarter lengths of whichmay be two `inches or less. linmy de\'icc,vthc 'waves from the tone armor` other source, are .irst'propagaled directly into and are partiallyexpanded in a one-dimension-expansion -conduit havingopposite walls thatare approximately parallel and may he slightly converging, provided onlythat they prevent substantial expansion in one dimension, Whilenotheropposite Walls are substantially diverging?r to afford guided expansionin the other dimensioni() the desired extent. As explained in my priorpatent, the parallels or expansion preventing walls of this part of theconduit are of best ,effect when not too far apart, that is, Aless than3 inches .and preferably less .than 2 inches. Propagation through such aonedimensionexpansion conduit seems to prepare Athe waves for dcflectionatright angles to the direction of expansion. that is, deflection in thedirection of thinness ofthe air column. Vhen the deflection is in thisdirection, there is less energy loss and phase displacement than i'vherethe deflection' isl in the direction of the expansion.l` Consequentlycurvestoi" other deleeting" surfaces', 1'deflect-ingl the sound beam inthe direction of its tliinness',:,inay he employed, and this' makespossible aclose `folding and 'a Vmassive integral construction presentinvention. i' l,

In .both of1 the forms herein showl fl'the amplier or projectori'stih'iis .folded in two 'versingl the ,direction of the jivaves' onelength Ainto the 'reverslely iiteiidingipoiftion.

"In the firstldescribedflfdrin,fthe 'de'iectorvdefleets the soundWaves'fromsthepriiary one- .described farm', 'the deflecfo turns thewaves into a project'orf,portion;,permittingrijderdirect-ion ofthethin'n'esi'siof thefpr skit-life..uhatlmayfbealle folded 'hiffnslbut1n the first '.forn'npne` of'jthefpara'llel; Walls of one foldlis`adjaceiit 'andconstructedfintev,g1-ny with' a: Waller lwaujof uit.text-foie whereas in thesecondjform it 'isig'meolfithe divergentzWallsj'of A one foldI thatj is adjacent one of t'heffparallelWallsofuthe other fold. The.I latter formgs analogousto that shown in myapplication `Ser. No. 679,911, filed Dec. 11, 1923, in that the Wideningeonduit has its outlet portion, curved in thedirection of its thinnessto discharge at any desired angle finto a Well developed projectorportion, the arrangement being preferably soford'eredv that the mainbeam' crosses the plane' of the Vvertical' mouth of the projector atasharp angle. This' abrupt turning is lin the .direction of thefthinnessof the sound beamandis guided by semicylindrieal surfaces,curvingTthrough an4 areI of approximately V18() degrees. .More'ov'len thewidening conduit may be curved in Athel direetion of itsvthinnesstln'ough a lessaicolf 90. degrees more or less, if desired.Y fThe above principles are lcapable vof embodiment in many specificallydifferent forms, but. I have'selected for villustration rig. 2,

Fig. 2 is a vertical .section on the, line .Q -2,

Fig. 3 is a front elevation.

Fig. 4 1s a view showing another form in vertical section along thecentral axis of the sound amplifier' and projector Aon the line 4 4,Fig. 5. Y Fig. 5 is a section on the line 5.-5, Fig.

l4, showing in dotted lines certain parts above the plane of thesection.

These drawings are intended to indicate approximate sizes as well as theproportions of the parts in one desirable embodiment of my invention.The scale is indicatgd at the top of each sheet. l

.In these drawings the'invention is shown as adapted for a cabinet typeof phonograph and in the first form the projector is adapted toform asolid base for such cabinet. In both forms a tone arm or other ,sourceof sound is supposed to discharge Idownward at the front of the cabinet.However, it is plain that by adding another fold to the form shown inFigures 1' and 2, the inlet to the projector would locate at the rear ofthe cabinet.

Y Referring to Figs. 1, 2 and 3, particularly l it will -be` seen thatthe device is mainly va wideningr conduit. The air column comprises aninlet portion a; a downwardly extending portion b, in which the aircolumn is prevented from expansion inrone dimension and may or may notbe slightly decreased in thickness; a horizontally extending portion cv,in which two opposite walls are parallel; a downwardly curving portion(l, in which the walls are concentric. semicylinders; a reverselyextendinghorizontal portionA e terminating in an outlet f. The inlet amay be of suitable diameter for receiving sound waves from a-suitableconduit and this may be a phonograph tone arm or a telephone receiver,say, one inch and three-quarters to vtwo inches in diameter andpreferably not more than three inches in diameter. While the contractionin the portion b is not essential, it is desirable to have it wherecompactness is desirable. since that makes possible the reduction ofthickness of the beam lin c to less than tivo inches, and if thisthickness is preserved throughout the partial expansion portion c,deecting portion d and reversely extending portion e, the total' size ofthe device for given lengt-h of air column, is proportionately reduced;The outletf is a more or less rudimentary mouthpiece lwhereby thetransition from the Widening conduit to the outer airfis rendered 'less`abrupt.

Referring to Fig. 1 it will be seen that the other two walls of theconduit widen practically uniformly from the inlet to the exit, theangle of divergence as shown being about 10 or 12 degrees. Preferablyfthe lengthfof vthe air column is l0 toa() inches and the `Width oftheoutlet 14 to 18 inches.

By thus limiting substantially all ofthe expansion of tliewvaveffro'nttonta .single dimension,'I am ,able lto get an adequate eX- pansionroffyv'ave front'andanlength of alir .column i(tlniee'or'fourllfeetfoiffmor in a vvery compact`space, thefwidth of the devicebeing .buffs'liffhly .gratrgthnn the width of the ont-let, t.the lengthhardly greater than one-half', ,the length fof the airncoluinn and theheight only fiveQor 'sin 'times thefthickness of said column..,Obvilousl'y'ffthe bends in. the direction jof fthe thiiinessf'of 1thelieo'nduit may 'be'v repeated fso thatf'tli'e conduit will be disposed'in :three orI more. lengths extending alternately inloppositeildirections and thebends maybe freateror less than degrees.The outletfvvidtlias ','well as the total 'length of theAlconduitmma'ybe greater lor less than showriiasmayI also the angles of'divergence ofthe lwallsft,l 637,17*.

what elliptical .instead` "of rectangular, rovided the thinner:dimension kept 'williin the 'desi1able limits, preferably about 2inches.l v l A widening, eoiiduit projector Vhaving theI abovecharacteristics may be leonstr'uetedin.

a variety of Ways. The simplest waylwould be to build it up from boardseach 'out to the proper shape, piled oneon top'of the other and gluedunder heavy pressure. As shown, however, the device somewhat lightenedby building i t'.froni two heavy boards forming thebotto1n1. and ltop 2.together with an intermediate spacer '3 having a fore and aft groove 4in whichslides an intermediate board 5. Between baseboard 1 andintermediate board 5 are heavy spacer strips, 6, Gaforming'the divergentwallsot the outlet half of the conduit while the divergent walls 7a ,maybe similarstrips primarily secured to thetop board 2. The inner end ofthe middle board f5 being' formed ona semi-cylindrical conve'Xit-yhaving a diameter of, say', l1 inch. the outer wall of the bend may becompleted b'yblock 8 having a corresponding inwardly directedsemi-cylindrical cavity 9 carried by' a cross- .piece 8a the endslofwhichslide in the grooves 4. ln thepresent .case this crosspiece isshown as longitudinally recessed to projecting portions 9a. 9a,embracing the ends of the dlvergent walls', y6, 7, 7a. All of throughthe lside ofthe cabinet.-

Y -Thc `tone arm or other tsource-0f sound dischargesat- 16 directlyvinto t-h'e: upper-:end .of .thefair column which-.extends continu-'ously- :thro'ughf theprimary? and secondary expansion conduits .to the;outer air.

.f'.l`.he"conduitz -\va,lls-are all ofvery. thick spruce, 'including thewalls .10, .10", .10 vand d of the widening conduit. These areall`atleast one'ineh; thick except the walllO, 'fthelou-eiend-of .which gisnradr tliin iiorder to. bringfzthe upperzwall of the .projector Vinpropel'. relation to theidischargefrom the curved end of `thewidening-.continit. Vibra- -tio'n .of-athis thinner,portion. however, is

-fill preventedby providing piers 10., preferably of gayood... TheseAare rfirmly ',gflued. between ltr-"and 10?,-.the.s'urfaces being drawn.into most .intimate--engagement while the glue is wet by zlneansof;tension -scre\\ts =10g. These scrmrs, prcferabl).Y pass freely through.holes 10 inlpiers =1 0.-\\fx thout'engaging. the sides of jsaid holes.1 This leaves the.end snr-facesI of .the-piei'sfreer; to -take andmaintain the desired'position under the clanjiping stress of the.sereutgaalso .unequalv lateralexpansion or contraction of thewoodcannot` t:il\'e.ell'ict directly on the screw. Similar piers may he usedforA the free edge .of the middle-wall in Figs. 2 and 2'.. but ish-ssnecessary because it is asier to malte this wall asA thick as maybedeired. i '[hej terminal portion of the. conduit also one inch spruce.The lengt-h ot the lower plate 2S is .such that it must be very .thickand stiff in order 'not to vibrate xunder the acoustiestresses -set upby proper funetiouing of (he projector as a whole.. .Hence I prefertomake the thickness of this plate greater. sa)v 1l/- inch. The sainetendencyA to vibrate is oundin the rooffplates 27 .and 10",

vlnut, these are ,so massively baekedin the present construction that.Vibration is minimized, if noteliminated.;v j he wavesemerginggfromtheconduit lll :are'diverg-ing on a spherical wave front and the angleis considerable- It results that Awhen the end-'walls-Othe terminalport-ion :part of leaclr flank of the. main" beam will ii'npinge uponsaid -walls and-will be thence reflected out of the mouth of theprojector. .ln most cases the thus'deected flanks of the beam will tend-to converge towardcrossing points far beyond the mouth of the projectorand practically the aiigles-are=insuicient for veffective lateraldiffusion' of-'the -sound on cach side of thedirect beam.- .While such arraugenient may beem'ployed for amy. present.- construction, Ihavefoundthat improved acousticfcifects, accompanied by.vgreater-'lateral diffusion-may be Aobtained byeon'verginer the endwalls as shown in Fig. 5. There .seems to be 2a further fadvantagedueto-conlining the :avayes-.laterally ..(a...sort.-of,-1r versat'offlankdifusion.)-,.particular 1 .where theYvertical.expansionfpermittediiir t is ,part of. .the conduit s isextremely-rapid. 'lhe oon-v .-\-'ergence lof thefpsi'de LWalls may-.be2small, not more f thanwsay" 10? #anywhere .toward 4the axis for each-wall'fandas fbefdreistafteda `the walls may be parallel.: 'i 1 a a,zal.. -For 'undistortediamplificati() findv hat the. wal-ls fof; thewidening .conduit'fas well ias of. the projectoi-shouldvverg'nStiff-andat .the eame-tin'xe ve1y-iligli t,'fsothat tendency@syi'npathetic vibrzltion'filwilli 'ididede and such .as may occunfwillfbe (1f-th her.- reduendes... To -thisendthe quaility'q fthema? aerial; used shouldibegn/ery stiff? and; .light 'as |96 .to-qua-lity,' wb-ile g'the. construction should be as. solid .-aspossible. ilon-ithis purpose -the best, material which Lhayefgbeenablebofind up to the present` time, is boards lor-timbers .of well seasoned ispru'efdlrobgblymthe .thicker the. timber isthehtter'iti'zould ,be, ,butexperience showsA that the aboyenamed -t-liiekness,of. an .ineli or tivoisq'iijactically. suf4 licient for; the -walls'o'fgtl ideningI conduit,.and .alsofortheprojector f "hile I- 4have shofwn ithefsemi-cylinder: at2l, 25, struckfronnp'oint gms-'the-centr'for turning. vthe waves..emerging fron'i the :slot out let of: widening,conduit:1m-,throughangli-s totaling`-180 degrees, itxvill beffo'und H0that other curved. or partly curved-*Yand iartly plane deflectors can beused'. Gurved surfaces' of; less .angular are or. .lessradius or struckv from .a more remote. center,A may be desirable..v lfvhcrethe conduitlOis vertical, 115 instead of' inclined at. a 45 degree angle; .a 'single'reflector may be used to turn-.the wavesthrough the degree angle,instead of two'- relleetors: for the. 180 .degree angle, and such single-reflectorgmayvbe-eitherplane-or l2" lcurved, -or.;partly plane andpartlyurved. These .and other similar modifications are based on myaboveexplained-principle that propagationof thev waves .between oppositejapproximatelyparallel wallsvxyhicli ip reveut 125 expansion in onedimension,with-other 011tlet walls diverging to permit guided-expansion-in the -other.ggliniensioru tq .Pfepare thesoundwaves-.foi-deflect-1QDJ-SQ -llfi j the conduit may becurved in.thedlrectionof 130 Aif() its thinness with less energy loss and phasedisplacement than where the deflection is in the other dimension.

My inventionv does not depend upon the correctness of my theories withreference. to it andin so far as I have. stated theories, it. has beenfor the purpose'of indicating or accounting'for novel results. W'hethercorrect or not, theywill be found useful as hy potheses to assist -thoseskilled in the art when seeking to apply one or more of my novel`principles to new conditions or purposes.V i i vlie-gardless oftheory.:it will be evidentv that. both formsl of the device shown in thedrawings-.are generically the same in that each embodies my novelcombination of the following fea-tures: Each embodies amassive-walledconduit affording an air column for amplifying andprojecting speech waves. 'which 4is folded upon itself as compa-ctly asmay be desired.

'lh'us, Figs-2- andfl are merely different` illnstrations'of how by 4myinvention, successive 'portions of the conduit may have 4oppositelyextending conduits or` walls `toldedadjacent each other without. 'dangerofdistortion and confusion by sympathetic vibration effects such asresult where the vibrations of the air column of one part of `aconduit-are permitted to strike through the adjacentwvall intoanother-part of the fair column, where the phase relations are entirely`different.

' InFig. 4, the mouth or projector portion starts much further back inthe conduit than in Fig. 2,' but the broad idea is the same and,

'as stated above, the deflecting 'curves or Abends in thedirection-ofthev thinner dimension of the conduit may be repeated todispose-any desired lengt-h of conduit in three 'or more lengthsextendingr in opposite directions, as in Fig. 2. Similarly, theprojector of Fig. 2 may have the wider area expansion and even thedesign of the projector portion of Fig. 4.

1n all forms of the device, it is highly important. to have allAsurfaces of the wood (preferably well seasoned spruce) filled andworked down to a very smooth hard finish. This 4is one reason why bothforms are .shown as of sectional construction. That of Figs. 1 i). and3, particularly, is adapted for complete finish of the interior surfacesbefore being assembled for final gluing or t-herwise securing togetherof parts. The layers may be built up one at a time from the bottom, eachinterior surface being polished before it is covered by the next layer.'or the building may-progress from top and bottom plates simultaneously.

1. ,A sound 'amplifying conduit for expandingthe wave fronts of complexsound Waves, said conduit being solidly constructed of thick, stiffmaterial, andcomprising walls arranged to permit wide expansion of -thewave front in one dimension along widely diverging lines and other wallsapproximately parallel with ea-ch other, arranged to guide said waves inthe other dimension, said conduit being curved in the direction of itsthinness approximately midway of its length. f

2. A sound amplifying conduit for expaiidingthe wave fronts of complexsound waves, said conduit being solidly constructed of thick,stiffmaterial, and comprising walls arranged-'to permitfwide expansion of-thewave front in .-onepdimension lalong widely diver-ging ylines andlot-her :walls: :approximately parallel wiith eachother, arranged toguide saidwavesfin the other dimension, Asaid conduit being.- curved .invthe direction of its thnness through an. are sutlicientto cause a wallof the conduit inadvance ofithe curve to constitute-a wallsfor a portionbeyond the .E .l r"., v I,-

A sound amplifying conduit. for.v expandingthe wave fronts-ofcomplexsound waves, said conduit being solidlyconstructed of thick, stili'materiahand comprising walls arranged Ato permit 'wide expansion of thewave front in onef-dimension along widely diverging lines andfothe'rWalls approximately parallel with eachother, arrangedA to guide saidwaves inf'the other dimension, said conduit being curved in thedirection of its thin'- ness through an arc-'ofapproximately 180degrees. 'I i' f f 4. A 'sound amplifying'conduit for expanding thewavefronts of'complex sound waves, said conduitfbeing solidly constructed ofthick, 'stlmateriahand comprising walls arranged to permit' wideexpansion of the Wave front in one dimension along widely diver-ginglines and other 'walls approximately parallel with each other, arrangedt-o guide said waves in the other dimension, said conduit being curvedin the direction of its thinness through an arc of approximately 180degrees approximately midway of its length.

5. A sound amplifying conduit for expanding the wave fronts of complexsound waves, said conduit beingr solidly constructed of thick, stiffmaterial, and con'iprising walls arranged to permit wide expansion ofthe wave front in one dimension along Widely diverging lines and otherwalls approximately parallel with each other, arranged to guit e saidwaves in the other dimension, said conduit being curved in the directionof its thinness through an are of approximately 180 degreesapproximately midway of its length a wall of conduit beyond the curveWaves,said conduit being .solidly constructed of'thick, stiff-material,and comprising a primary vportion having walls arranged to permit guidedand' limited but rapid eX pansion of thefwave front in one dimensionalong ,widely diverging lines and other walls nearly parallel-with eachother, arranged to guide said wav'es in the other dimension, .therebyforming'la thin sound beam with Widely divergentflanks and a' deeplycurved wave. front; the .outlet endfof said` primary expansion beingcurvedin the direction ofvits thinnessfand discharging into' a projectorportion having-walls diverging at an angle permitting guided i @but-rapid ,f expansion of L." saidfbeam:finnsaidnsecondtdimensionn -.-'7';.A sound :amplifying *.oonduitv. for ..ex pandnga-the-. wave frontsoficomplex sound waves, said'conduitlbeing solidly .constructed ofthickgz'stiffi material,iandcomprising za primary' expansion f. portionhaving. :wallsfy arrangedf to ,.permit T iguided `and limited `but rapidexpansionlbf the-gwavefront in one dimension along widely diver-ginglinesand other -w'alls vnearly; Eparallel with eacliother, arranged.tovv guide -said ywaves in. -the'fother dimension,-tliereby Eforming-al.thin sound beamV with widely divergent fla-nl'is and a deeplycurved-:Wave:frontgf the outlet endA of said primary expansion portionbeing curved in the :direction fof.. its i thinnessthrough an angleofIappioximately .180:degrees and dis# charging iin the; direction ofy adivergentwvall of iaj .projector portion l having@ walls' diverging atanangleipermittingfguided but rapid expansion;=ofsaid=beam insaid.secondfdimension. i

. 8.1A soundlamplifying` econduit ,forcx' panding the=wave frontsof'compljex waves, saidlconduit .beingfsolidly constructed of 1,-.;thick, trigidmat'erial and being-.reversely folded upon' itself to formsuccessive,` adjacentv lengths or .folds' extending in oppositedirections, adjacent surfaces of adjacent folds being vopositesurfacesfof the samewall l of thiclnrigid material; saidvfolds includ-y ing aprimary expansiongport-ion having opposite divergent Walls arranged topermit guided expansion; of vthe-Wave front in one dimension and otheropposite walls nearly parallel with each other'arranged to confine saidWaves in the other dimension, thereby forming a relatively thin soundbeam comprising Waves projected along lines widely diverging in thefirst dimension but with little or no divergence in the seconddimension; and the fold into which said primary expansion portiondischarges embodying a reversely extending projector portion havingwalls widely diverging in said second dimension and one of which is thesame Wall of thick, rigid material that forms a Wall of the adjacentprimary expansion portion; and the primary expansion portion beingconnected with the projector portion by a defiector which is thick,rigid material and has deflecting surfaces curved in the direction ofthinness of the sound beam to substantially reverse the direction ofsaid beam.

f9. A sound amplifying conduit for expanding the Wave fronts of complexwaves, said conduit being solidly constructed of stiff material .andbeing reversely folded upon itself to form successive, adjacent lengthsor folds extending in opposite directions, adjacent surfaces ofthefirst. of said folds being fiattened to afford partial expansion of theWaves,'much greater. in one dimension than in the other, .adjacent foldsbeingbpposite surfaces of the same solid wall'of stiivmaterial, Vand.successive 1opposite` folds being connected by la :defiectorwhichis=offstii materiall ancLy has` deflecting surfaces curved inthedirection gofathin dimension of the conduit. ff;

` panding-,the wave front. ofcomplex waves,-

said conduit being solidlylconstructed of stii materialfandbeingreversely folded iupon itselftoI form successive,.=-contiguous lengthsor folds extending in opposite directionsfand embodying a primary..expansiom portion having .two opposite` sides approximately parallelandi-two ,other sides substantially diverging, the" successiveoppositely extending .folds vbein .connected by a deflector, thedefiecting sur acesvoffwhich operate by lateraldeflectionlin;the;direction of the thin dimension of` the' conduit, tosubstantially reverse the direction of thesound vWaves forpropagationthrough a projector having divergent walls permittingexpansion in the direction-of'such deection. i j.

l1. Afsound amplifying eonduit.,fo1-ex. panding the AWavefrontsofcomplex waves, said -conduit .being .solidly .constructed ofrigid material and-.being reversely folded upon itselfgto formsuccessive, contiguous lengths or folds extending in oppositedirections, said folds including a primary `expansion portion havingopposite divergent .Walls arranged to permit guided expansion of thewave front in one dimension `and other opposite walls nearly parallel-With each other arranged to confine said Waves in the other dimension,thereby forming a relatively thin sound beam comprising Waves projectedalong lines Widely diverging in the first dimension but With little orno divergence in the `second dimension; vand the fold into which saidprimary expansion portion discharges embodying a reversely extendingprojector portion having walls Widely diverging in said seconddimension; and the primary expansion portion being connected with theprojector portion by a deiector, the deflecting surfaces of whichoperate in the direction of thinness of the sound beam to substantiallyreverse the direction of said beam. -i

12. An amplifying conduit for guidi-ng, expanding and projecting complexwaves into the atmosphere, said conduit being solidly constructed ofstiff material and reversely folded upon itself, with the adjacent wallsof adjacent, oppositely extending folds laterally united as a 'massiveintegral structure, ;0 as to minimize sympathetic vibration; saidconduit including a conduit section, for partial one dimension expansionof the waves, having opposite walls that are substantially parallel tosubstantially prevent expansion in one dimension and other'oppositeWalls substantiallly diverging to permit expansion in the otherdimension; also another conduit section, foi* further onedirnension'expansion ofthe waves from the first sectioii,'liavingopposite walls to prevent expansion in one dimension and otherfoppositewallstopermit the expansion in the other dimension; alsoincludingdeiectinji surfacearranged to deflect the partiallyjexpandedwaves from said first mentioned conduit sectioiriu the direction of thethinner'dimensionithereof.

13. An amplifying conduit forfguicling, expanding and projecting complexwaves in-- to the atmosphere, said conduit being solid-y ly constructedof stiff material and reversely folded upon itself,f`with the adjacentWalls of adj acent, oppositely extending folds vlaterally united asamassive integral structure, so as to minimize syn'ipathetic'vibration;said conduit including a conduit' section, for partial one dimensionexpansion of the Waves, having opposite Walls'that are substantiallyparallel to substantialljlv prevent expansion in one dimension and-'otheropposite Walls substantially divergingfto permit expansion in theother dimensiongzalso another conduit section. for furtherfone dimension'expansion -of the waves from the (irst'section, having opposite wallsto prevent expansion in one dimension and other opposite Walls to permitthe expansion in the other dimension: also including smoothl)r curvingdefiecting surface arranged to defiert the partially expanded Waves fromsaid first mentioned conduit section in the direction of the thinnerdimensin thereof; the laterally reversely folded upon itself, with thead-4 jacent Walls of adjacent, oppositely extendlng folds laterallyunited as a massive integral structure so as vto minimize sympatheticvibration; said conduit including a conduit section formed. for lpartialexpansion of the waves in one dimension more than in theother;.anothericonduit section formed for further expansion of =saidwaves from the first mentioned conduit section in the direction ofthethinner dimension thereof; and`^includingalso deflecting-surface ar`ranged to -deect the partially expanded waves from said first mentionedconduit section in the direction of said-thinner dimension. l f' 15. Anamplifying conduit for guiding, ex panding and projecting complex wavesinto the atmosphere, said conduit being reversely folded upon litself,the. adjacent, oppositely extending folds having the inlet. end of thewall of one fold and the outlet end of the next fold laterallyunited asa massive integral structure so. as to' minimize sympathetic vibration;Asaid conduit including a conduit-'section formed for. partial expansionof Athe vWaves in ione dimension 'more thanY in the' other; anotherconduit section formed for further expansion of said waves from thefirst lmentioned conduit lsection in the direction of the thinnerdimension thereof: and including also intermediate deectingsurfacearranged to deflect the partially expanded Waves from said firstmentioned conduit section in the direction of said thin ner dimension. e

Signed at Buffalo in the county of Erie and State -of New York' this10th day of Decemher, A. D. 1923.

ELWoon GRISSINGER.

